Should we ban the Griffin Conservatory and the Hive of Serpents?

Even if one player gets 3 minimal Gnomish units, and another gets 7 more powerful ones, it's hard to argue that this is less critical.

How does this support the statement

In my opinion, weaker bonuses are distributed much more evenly.

?

Then let's cancel all the restrictions.

The current restrictions, unlike what you're suggesting, are designed to eliminate imbalances that exist regardless of randomness. Without them, Necropolis and Fortress would barely be playable, except against each other.